1.1. BACKGROUND
Sealed radioactive sources (SRSs) are used extensively in agriculture, industry, medicine and various research areas in both developed and developing Member States. Virtually, all countries utilize radioactive SRSs for one purpose or another. The total inventory of SRSs worldwide is estimated to be in the millions. Despite their predominantly small physical size, many sources contain very high concentrations of radionuclides (industrial and medical sources are typically in the GBq to PBq range). The radiation emitted from these sources is quite intense, requiring heavily shielded containers for their safe use, transportation and storage.
A radioactive source that is no longer in use or not intended to be used, for the practice for which an authorization has been granted, is termed as disused [1]. If a source is no longer suitable for its intended purpose as a result of radioactive decay, it is considered as spent. It is important to emphasize that a source declared by one user as disused may still be used by a different user, supplier or manufacturer. A disused or spent SRS may still be highly radioactive and potentially hazardous to human health and the environment. The nature and magnitude of the various problems associated with disused SRSs are addressed in Ref. [2].
Although the vast majority of radioactive sources used around the world are managed safely and securely, bringing many benefits to humankind, a number of accidents involving radioactive sources have occurred [3–10].
Where the amount of radioactive material is substantial, as in the case of radiotherapy sources or industrial radiography sources, the accidents have resulted in severe or even fatal consequences [3, 5]. The majority of accidents were related to SRSs in use, which were still under regulatory control, but several accidents have occurred with disused sources when regulatory control was weak or totally absent. Some of these accidents have resulted in contamination of large areas that required costly clean-up operations for mitigation of the consequences of such accidents [3].
In order to reduce the risks associated with disused sealed radioactive sources (DSRSs), it is important to have a well-developed national strategy, legal framework and infrastructure for their safe management both at the user’s site and in the entire country. It is essential that sources that either are in use, or declared disused, do not pose any potential hazard to the workers, the general public or the environment. Ideally, all requirements for the safe management of DSRSs need to be enforced and implemented, prior to initiating any particular application of SRSs in a Member State.
Countries lacking comprehensive infrastructure for radiation protection and waste management systems may not be cognizant of the risks associated with disused radioactive sources. Even some developed countries that use SRSs extensively may underestimate the risks involved and, thus, may not have fully effective control of their radioactive sources, even though they have adequate legislation, radiation protection and a waste management system in place [9]. Other countries do not give high enough priority to DSRS management programmes because there are more urgent issues demanding their available resources. Even if the risks associated with using SRSs are recognized, there are still significant potential risks associated with disused SRSs.
The number of disused radioactive sources in a given Member State does not influence the consequences of an individual accident, but increases the likelihood that an accident will occur. The degree of regulatory control and its effectiveness also influence the probability of an accident. The consequences of such accidents are governed by the characteristics of the source (source design, activity, chemical form etc.), nature of the accident, people involved, countermeasures taken, etc.
In the 1990s, there was growing international concern about radioactive sources, which for one reason or another, were not subject to regulatory control or over which regulatory control had been inadequate. The IAEA programme on DSRS was established in 1991 with the specific purpose to assist Member States in their effort to avoid situations that might result in unnecessary radiation exposure or accidents. The programme includes provision of technical assistance to Member States in the form of IAEA’s technical reports, training of experts and development or improvement of the required infrastructure by provision of tools, equipment and transfer of technology through the IAEA’s appraisal service for evaluating a Member State’s radiation safety regulatory framework.
In 2011, the IAEA published the General Safety Requirements publication, IAEA Safety Standards Series No. GSR Part 3, Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards,
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Interim Edition (hereafter BSS) [11]. This publication supersedes the International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, which was issued in 1996 [12].
A binding international legal instrument for radioactive waste management has been established through the Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management (hereafter the Joint Convention) [13]. Under Article 28 of the Joint Convention, Contracting Parties are required to ensure that the possession, remanufacturing or disposal of disused sealed sources takes place in a safe manner, and Contracting Parties allow for re-entry into its territory of DSRS (if accepted in the framework of its national law).
The IAEA has also published the Code of Conduct on the Safety and Security of Radiation Sources (thereafter Code of Conduct) [14]. The objectives of the Code of Conduct are, through the development, harmonization and implementation of national policies, laws and regulations, and through the fostering of international cooperation, to:
— Achieve and maintain a high level of safety and security of radioactive sources;
— Prevent unauthorized access or damage to, and loss, theft or unauthorized transfer of, radioactive sources, so as to reduce the likelihood of accidental harmful exposure to such sources or the malicious use of such sources to cause harm to individuals, society or the environment;
— Mitigate or minimize the radiological consequences of any accident or malicious act involving a radioactive source.
The IAEA continues to explore ways to improve its radioactive waste management programme to support various Member States. One new initiative is specifically related to the end of life management of DSRSs; including when disused sources are managed as radioactive waste. Until recently, the emphasis was primarily on the safety of radioactive sources, with source security as one aspect of safety. However, given the potential for the use of radioactive sources in malevolent acts, source security has taken on a new urgency. The new approach of cradle-to-grave control of radioactive sources can provide protection against malevolent uses. This includes consideration of security during the entire life cycle of radioactive sources, covering all phases, including manufacture, distribution, installation, commission, usage, storage and disposal, is of paramount importance.
1.2. OBJECTIVE
The main objective of this report is to provide reference material and technical guidance on the safe management of DSRSs, covering all aspects, including handling, conditioning, transportation, storage and disposal.
It is anticipated that this report will be useful and of direct relevance to various stakeholders, including policy makers, users of SRSs, operators of waste management facilities and regulatory bodies, particularly in Member States that are exploring options or developing strategies for the safe management of DSRSs. It is intended to respond to the needs of various Member States in the management of disused sources, ranging from countries that have a relatively well developed radioactive source management infrastructure and regulatory framework to countries that are in a very early stage of conceptual planning for the management of disused radioactive sources.
1.3. SCOPE
This report presents information on the management of DSRSs, based on the information compiled in a series of earlier IAEA technical publications issued between 1990 and 2003 [2, 15–19]. However, the information in those publications has been reviewed and has been improved with the inclusion of new management techniques acquired in recent years.
The scope of this report covers all types of DSRSs, except those exempted from regulatory control, e.g. watches or instrumentation dials. However, the report does include smoke detectors and other low activity sources, which have been exempted from regulatory control as individual sources but after collection can represent a significant risk and thus require safe management. It discusses, in some detail, various approaches, options and procedures for the handling, conditioning, transportation, storage and disposal of DSRSs, and the associated management system requirements. Some problems encountered and lessons learned are included for every waste management step.
1.4. STRUCTURE
This report comprises 14 sections and one annex. Sections 2–6 deal with the general issues of DSRS management, while Sections 7–12 review the main steps of DSRS management in consecutive order. The consecutive order refers to an ideal DSRS management scenario, when all the institutions, facilities and personnel are in place. Of course, this situation rarely exists in most of the Member States; however, this approach provides the benefit of showing the ideal DSRS management scenario. At the end of each section dealing with a separate DSRS management step, some examples are provided together with appropriate lessons learned.
Section 2 outlines the key radiological, physical and chemical characteristics of sealed radioactive sources, which are important in the selection of appropriate management options for the sources.
Section 3 provides general information on the current international approaches to categorization and classification of SRSs.
Section 4 describes the devices together with associated sources that are used in various applications, keeping in mind that a good understanding of the specific application of the source and used equipment are an important consideration in developing a strategy for the management of disused sources.
Section 5 presents the basic elements of a national system for the safe management of disused radioactive sources, including legal, regulatory and licensing aspects, technical capabilities, and financing mechanisms and describes the elements of a modern management system applied in all activities. This section also describes the main reasons and rationale for declaring an SRS ‘disused’ or ‘spent’.
Section 6 discusses an approach for selecting a strategy for the management of disused radioactive sources and describes various key management options.
Section 7 deals with the characterization of sealed radioactive sources by various non-destructive and destructive methods and emphasize the role of characterization in the selection of a safe and secure management option.
Section 8 addresses the handling procedures, equipment and tools used at different stages of DSRS management.
Section 9 addresses the storage of unconditioned disused sources at user’s premises as well as the storage of conditioned DSRS at central stores, with particular emphasis on the design features of a waste package accepted for storage and design requirements for a storage facility, emphasizing the importance of safety assessment for such facilities. It also provides a summary of the approaches used, including a description of specific processes, for the storage of high activity sources.
Section 10 deals with conditioning of different types of disused sources. It begins with the conditioning requirements, including design, operation and records keeping. It also discusses recommendations for the selection of an appropriate conditioning methodology, including a description of various conditioning methods.
Section 11 examines the transportation of disused radioactive sources, introducing the IAEA transport regulations, and addresses transportation problems that are unique to high activity radioactive sources. Some transportation options are also discussed.
Section 12 deals with the disposal options for disused radioactive sources, including a discussion of the specific characteristics of radioactive sources that present a problem for their disposal. It also presents a review of problems encountered and lessons learned, and discusses the borehole disposal concept as a potentially promising option.
Section 13 describes the role of safety assessments throughout the lifetime of the facility or activity whenever the designers, constructors, manufacturers, operating organization or regulatory body should make decisions on the management options and related safety issues. It also represents briefly the process for the development of safety assessments.
Section 14 summarizes the achievements in the management of disused radioactive sources, emphasizing some activities that are important in addressing the problematic issues.
The Annex addresses the radiological risks associated with disused sources, in particular where control was inadequate or completely lost. Some accidents with disused sources are briefly discussed.
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